USMLE® Step 1 Question of the Day: Frank-Starling curve

USMLE® Step 1 Question of the Day: Frank-Starling Curve

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A patient’s resting Frank-Starling curve is shown below and denoted as Curve 1. Which of the following scenarios would cause the patient’s Frank-Starling curve to more closely resemble that denoted by Curve 2?

Frank-Starling curve and how certain scenarios can alter its shape in patient's cardiovascular health.

A. Heart failure

B. Propranolol administration

C. Dilated cardiomyopathy

D. Dobutamine administration

E. Myocardial infarction

Scroll down for the correct answer!

The correct answer to today’s USMLE® Step 1 Question is…

D. Dobutamine administration

Before we get to the main explanation, let’s look at the explanations for the incorrect answers. Skip to the bottom if you want to see the correct answer right away!

Incorrect answer explanations

A. Heart failure

Incorrect: Heart failure would result in reduced cardiac contractility, which would shift the curve downwards and to the right. In contrast, this question is looking for a factor that would shift the curve upwards and to the left.

B. Propranolol administration

Incorrect: Propranolol is a β-blocker that reduces cardiac contractility, which shifts the curve downwards and to the right. In contrast, this question is looking for a factor that would shift the curve upwards and to the left.

C. Dilated cardiomyopathy

Incorrect: Dilated cardiomyopathy is a condition wherein the heart becomes enlarged and cannot pump blood effectively. The condition would result in reduced cardiac contractility, which would shift the curve downwards and to the right. In contrast, this question is looking for a factor that would shift the curve upwards and to the left.

E. Myocardial infarction

Incorrect: A myocardial infarction can lead to cardiac tissue injury and death. These changes would likely result in reduced cardiac contractility and cause the Frank-Starling curve to shift downwards and to the right.

Main Explanation

The Frank-Starling mechanism describes the relation between end-diastolic volume (EDV) and stroke volume (SV). 

Factors that increase cardiac contractility, also known as inotropy, cause the curve to shift upwards and to the left. Examples of such factors include exercise, increased catecholamine release (e.g., fight-or-flight response), and inotropic medications (e.g., dobutamine, milrinone, and digoxin). 

In contrast, factors that decrease cardiac contractility will cause the curve to shift downwards and to the right. Examples of such factors include heart failure, loss of functional myocardium (e.g. myocardial infarction), dilated cardiomyopathy, and medications that decrease inotropy (e.g., β-blockers, calcium channel blockers).

illustration of frank starling relationship and effects

Major Takeaway

The Frank-Starling mechanism describes the relation between end-diastolic volume and stroke volume. Factors that increase cardiac contractility will lead to an upward and leftward shift of the curve. In contrast, factors that decrease cardiac contractility will lead to a downward and rightward shift of the curve.

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The United States Medical Licensing Examination (USMLE®) is a joint program of the Federation of State Medical Boards (FSMB®) and National Board of Medical Examiners (NBME®). Osmosis is not affiliated with NBME nor FSMB. 


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